diff --git a/src/ui/mod.rs b/src/ui/mod.rs
index d8e2d81..04dda25 100644
--- a/src/ui/mod.rs
+++ b/src/ui/mod.rs
@@ -4,6 +4,7 @@ pub mod preset;
 
 use bevy::prelude::*;
 use bevy_egui::egui;
+use egui::{LayerId, UiBuilder};
 
 use crate::ui::preset::{Preset, apply, canonical_hash, params_hash};
 use crate::ui::style::ACCENT_CYAN;
@@ -139,179 +140,120 @@ pub fn ui_system(
     mut camera: ResMut<crate::camera::OrbitCamera>,
     mut wants: ResMut<crate::camera::WantsPointer>,
     mut planet_dirty: ResMut<crate::scene::planets::PlanetSystemDirty>,
+    mut current_preset: Local<Preset>,
+    mut just_applied: Local<bool>,
+    mut last_hash: Local<Option<u64>>,
 ) {
-    if let Ok(ctx) = contexts.ctx_mut() {
-        egui::Window::new("Controls")
-            .collapsible(true)
-            .resizable(true)
-            .default_pos([16.0, 16.0])
-            .default_width(300.0)
-            .default_height(560.0)
-            .show(ctx, |ui| {
-            egui::ScrollArea::vertical().show(ui, |ui| {
-                egui::CollapsingHeader::new("Camera")
-                    .default_open(true)
-                    .show(ui, |ui| {
-                        ui.add(egui::Slider::new(&mut camera.distance, 3.0..=200.0).text("Distance"));
-                        ui.add(egui::Slider::new(&mut camera.yaw, -std::f32::consts::PI..=std::f32::consts::PI).text("Yaw"));
-                        ui.add(egui::Slider::new(&mut camera.pitch, (-std::f32::consts::PI + 0.05)..=(std::f32::consts::PI - 0.05)).text("Pitch"));
-                        ui.add(egui::Slider::new(&mut camera.fov, 0.3..=2.0).text("FOV"));
-                    });
-                egui::CollapsingHeader::new("Black Hole")
-                    .default_open(true)
-                    .show(ui, |ui| {
-                        ui.add(egui::Slider::new(&mut params.spin, 0.0..=1.0).text("Spin (χ)"));
-                        ui.label(format!("ISCO (disk inner): {:.3}", crate::physics::kerr_isco(params.spin)));
-                        ui.label(format!("Horizon r+: {:.3}", crate::physics::kerr_horizon(params.spin)));
-                    });
-                egui::CollapsingHeader::new("Accretion Disk")
-                    .default_open(true)
-                    .show(ui, |ui| {
-                        // disk_inner removed — now spin-derived (see Black Hole section).
-                        ui.add(egui::Slider::new(&mut params.disk_outer, 6.0..=50.0).text("Outer radius"));
-                        ui.add(egui::Slider::new(&mut params.disk_tilt, 0.0..=std::f32::consts::PI).text("Tilt"));
-                        ui.add(egui::Slider::new(&mut params.disk_brightness, 0.0..=3.0).text("Brightness"));
-                        ui.add(egui::Slider::new(&mut params.disk_rotation_speed, 0.0..=3.0).text("Rotation speed"));
-                        use crate::params::DiskColorMode;
-                        let mut cm = params.disk_color_mode;
-                        egui::ComboBox::from_label("Color model")
-                            .selected_text(format!("{:?}", cm))
-                            .show_ui(ui, |ui| {
-                                ui.selectable_value(&mut cm, DiskColorMode::Gradient, "Gradient");
-                                ui.selectable_value(&mut cm, DiskColorMode::Blackbody, "Blackbody");
-                            });
-                        params.disk_color_mode = cm;
-                        ui.add_enabled(
-                            cm == DiskColorMode::Blackbody,
-                            egui::Slider::new(&mut params.disk_temp, 1000.0..=50000.0).text("Temperature (K)"),
-                        );
-                    });
-                egui::CollapsingHeader::new("Planets")
-                    .default_open(false)
-                    .show(ui, |ui| {
-                        // Record state before edits; if seed/count/k/enabled change,
-                        // flag dirty so spawn_planet_system regenerates next frame.
-                        // (time_scale excluded: it only scales orbit_system's time,
-                        //  no respawn needed.)
-                        let prev = (
-                            params.planets_enabled,
-                            params.planet_count_target,
-                            params.planet_radius_factor,
-                            params.planet_seed,
-                        );
-                        ui.checkbox(&mut params.planets_enabled, "Enable");
-                        ui.add(egui::Slider::new(&mut params.planet_count_target, 0..=8).text("Count"));
-                        ui.add(egui::Slider::new(&mut params.planet_radius_factor, 1.1..=2.0).text("Radius (× disk outer)"));
-                        ui.label(format!("Orbit r = {:.2} (disk outer: {:.1})", params.planet_radius_factor * params.disk_outer, params.disk_outer));
-                        ui.add(egui::Slider::new(&mut params.planet_seed, 0..=1000).text("Seed"));
-                        ui.add(egui::Slider::new(&mut params.planet_time_scale, 1.0..=200.0).text("Time scale"));
-                        let curr = (
-                            params.planets_enabled,
-                            params.planet_count_target,
-                            params.planet_radius_factor,
-                            params.planet_seed,
-                        );
-                        if curr != prev {
-                            planet_dirty.0 = true;
-                        }
-                    });
-                egui::CollapsingHeader::new("Disk Turbulence")
-                    .default_open(true)
-                    .show(ui, |ui| {
-                        use crate::params::DiskQuality;
-                        let mut q = params.disk_quality;
-                        egui::ComboBox::from_label("Disk quality")
-                            .selected_text(format!("{:?}", q))
-                            .show_ui(ui, |ui| {
-                                ui.selectable_value(&mut q, DiskQuality::Off, "Off");
-                                ui.selectable_value(&mut q, DiskQuality::Low, "Low");
-                                ui.selectable_value(&mut q, DiskQuality::Medium, "Medium");
-                                ui.selectable_value(&mut q, DiskQuality::High, "High");
-                            });
-                        params.disk_quality = q;
-                        let on = q != DiskQuality::Off;
-                        ui.add_enabled(on, egui::Slider::new(&mut params.disk_half_thickness, 0.02..=0.3).text("Thickness (H/R)"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.filament_freq, 0.2..=4.0).text("Filament frequency"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.filament_sharpness, 1.0..=6.0).text("Filament sharpness"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.density_freq, 0.2..=3.0).text("Density frequency"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.density_strength, 0.0..=2.0).text("Density strength"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.arm_count, 0.0..=6.0).text("Arm count"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.arm_tightness, 0.0..=6.0).text("Arm tightness"));
-                        ui.add_enabled(on, egui::Slider::new(&mut params.arm_strength, 0.0..=1.0).text("Arm strength"));
-                    });
-                egui::CollapsingHeader::new("Doppler").show(ui, |ui| {
-                    ui.checkbox(&mut params.doppler_enabled, "Enabled");
-                    ui.add_enabled(params.doppler_enabled, egui::Slider::new(&mut params.doppler_strength, 0.0..=3.0).text("Strength"));
-                });
-                egui::CollapsingHeader::new("Jets").show(ui, |ui| {
-                    ui.checkbox(&mut params.jets_enabled, "Enabled");
-                    // Mirror the shader's spin gate (sample_jets in black_hole.wgsl):
-                    // jets are a spin-powered (Blandford-Znajek) outflow and render
-                    // only for χ ≥ 0.05. When the user enables them at low spin,
-                    // explain the no-op so the checkbox doesn't look broken.
-                    let jets_renderable = params.spin >= 0.05;
-                    if params.jets_enabled && !jets_renderable {
-                        ui.label("Spin (χ) too low — jets need χ ≥ 0.05.");
-                    }
-                    ui.add_enabled(
-                        params.jets_enabled && jets_renderable,
-                        egui::Slider::new(&mut params.jets_strength, 0.0..=3.0).text("Strength"),
-                    );
-                });
-                egui::CollapsingHeader::new("Renderer").show(ui, |ui| {
-                    ui.add(egui::Slider::new(&mut params.steps, 50..=600).text("Steps"));
-                    ui.add(egui::Slider::new(&mut params.render_scale, 0.25..=1.0).text("Render scale"));
-                });
-                egui::CollapsingHeader::new("Background").show(ui, |ui| {
-                    ui.add(egui::Slider::new(&mut params.star_intensity, 0.0..=3.0).text("Star intensity"));
-                    ui.add(egui::Slider::new(&mut params.skybox_intensity, 0.0..=3.0).text("Skybox intensity"));
-                });
-                egui::CollapsingHeader::new("Grid").show(ui, |ui| {
-                    ui.checkbox(&mut params.grid_enabled, "Enabled");
-                    ui.add_enabled(params.grid_enabled, egui::Slider::new(&mut params.grid_density, 0.1..=4.0).text("Density"));
-                });
-                egui::CollapsingHeader::new("Quality")
-                    .default_open(true)
-                    .show(ui, |ui| {
-                        use crate::params::BloomQuality;
-                        let mut q = params.bloom_quality;
-                        egui::ComboBox::from_label("Bloom quality")
-                            .selected_text(format!("{:?}", q))
-                            .show_ui(ui, |ui| {
-                                ui.selectable_value(&mut q, BloomQuality::Off, "Off");
-                                ui.selectable_value(&mut q, BloomQuality::Low, "Low");
-                                ui.selectable_value(&mut q, BloomQuality::Medium, "Medium");
-                                ui.selectable_value(&mut q, BloomQuality::High, "High");
-                            });
-                        params.bloom_quality = q;
-                        ui.add_enabled(q != BloomQuality::Off, egui::Slider::new(&mut params.bloom_threshold, 0.0..=3.0).text("Bloom threshold"));
-                        ui.add_enabled(q != BloomQuality::Off, egui::Slider::new(&mut params.bloom_strength, 0.0..=2.0).text("Bloom strength"));
-                        ui.add(egui::Slider::new(&mut params.exposure, 0.5..=3.0).text("Exposure"));
-                        ui.add(egui::Slider::new(&mut params.render_scale, 0.25..=1.0).text("Resolution scale"));
-                        ui.checkbox(&mut params.star_aa, "Anti-aliased stars");
-                        {
-                            // Per-pixel supersampling: antialiases the higher-order
-                            // lensed-image rings on the disk into a smooth gradient.
-                            // Cost scales linearly with sample count (each sub-ray
-                            // runs the full RK45 march).
-                            use crate::params::AaQuality;
-                            let mut a = params.aa_quality;
-                            egui::ComboBox::from_label("Ring anti-alias")
-                                .selected_text(format!("{:?} ({}×)", a, a.samples()))
-                                .show_ui(ui, |ui| {
-                                    ui.selectable_value(&mut a, AaQuality::Off, "Off (1×)");
-                                    ui.selectable_value(&mut a, AaQuality::Low, "Low (2×)");
-                                    ui.selectable_value(&mut a, AaQuality::High, "High (4×)");
-                                });
-                            params.aa_quality = a;
-                        }
-                        ui.label("MSAA is decorative on a fullscreen shader (no geometry edges to sample).");
-                    });
-            });
-            });
-        // egui captures pointer when the cursor is over a window or being interacted with.
-        wants.0 = ctx.egui_wants_pointer_input();
-    } else {
+    // Local<Preset> defaults to Custom (Preset::default()).
+    // Local<Option<u64>> defaults to None — first-frame sentinel.
+
+    let Ok(ctx) = contexts.ctx_mut() else {
         wants.0 = false;
+        return;
+    };
+
+    // --- Custom-detection (skip on the frame a preset was just applied) ---
+    let now_hash = params_hash(&params);
+    if !*just_applied && last_hash.is_some() && now_hash != last_hash.unwrap() {
+        // Some preset-touched field changed by hand. If it no longer matches
+        // the current concrete preset's canonical bundle, flip to Custom.
+        let matches_any = matches!(
+            *current_preset,
+            Preset::Cinematic | Preset::Performance | Preset::Web
+        ) && canonical_hash(*current_preset) == now_hash;
+        if !matches_any && *current_preset != Preset::Custom {
+            *current_preset = Preset::Custom;
+        }
     }
+    *just_applied = false;
+    *last_hash = Some(now_hash);
+
+    // --- Chassis ---
+    // egui 0.35's Panel::show needs a parent `&mut Ui`, but bevy_egui's
+    // single-pass `EguiPrimaryContextPass` only hands us a `Context`. Create
+    // the top-level Ui manually (matches bevy_egui 0.41's side_panel example).
+    // `Context` is an `Arc`, so cloning it here is cheap.
+    let mut root_ui = egui::Ui::new(
+        ctx.clone(),
+        "controls_root".into(),
+        UiBuilder::new()
+            .layer_id(LayerId::background())
+            .max_rect(ctx.viewport_rect()),
+    );
+    egui::Panel::right("controls")
+        .default_size(300.0)
+        .size_range(260.0..=400.0)
+        .resizable(true)
+        .show(&mut root_ui, |ui| {
+            // Top bar (fixed).
+            preset_bar(ui, &mut params, &mut current_preset, &mut just_applied);
+
+            // Section stack (scrolls).
+            egui::ScrollArea::vertical().show(ui, |ui| {
+                use crate::ui::sections::*;
+
+                // --- Always-open cards ---
+                group(ui, "Camera", |ui| section_camera(ui, &mut camera));
+                group(ui, "Black Hole", |ui| section_black_hole(ui, &mut params));
+                group(ui, "Accretion Disk", |ui| section_disk(ui, &mut params));
+                group(ui, "Quality", |ui| section_quality(ui, &mut params));
+
+                // --- Collapsing sections ---
+                collapsing(ui, "turbulence", "Disk Turbulence", false,
+                    |ui| section_turbulence(ui, &mut params));
+
+                // collapsing_with_toggle takes `&mut bool` for the header
+                // checkbox AND a body closure that mutates `params`. Passing
+                // `&mut params.<field>` plus a closure borrowing `&mut params`
+                // is a double-mutable-borrow; copy the field out, pass a local
+                // ref, then write it back. (All four are `bool` → Copy.)
+                let mut en = params.doppler_enabled;
+                collapsing_with_toggle(ui, "doppler", "Doppler", false,
+                    &mut en,
+                    |ui, en| section_doppler(ui, &mut params, en));
+                params.doppler_enabled = en;
+
+                let mut en = params.jets_enabled;
+                collapsing_with_toggle(ui, "jets", "Jets", false,
+                    &mut en,
+                    |ui, en| section_jets(ui, &mut params, en));
+                params.jets_enabled = en;
+
+                // Planets: snapshot dirty-relevant fields before rendering so
+                // we can detect changes (relocated from the old Planets block).
+                let prev_planet = (
+                    params.planets_enabled,
+                    params.planet_count_target,
+                    params.planet_radius_factor,
+                    params.planet_seed,
+                );
+                let mut en = params.planets_enabled;
+                collapsing_with_toggle(ui, "planets", "Planets", false,
+                    &mut en,
+                    |ui, en| section_planets(ui, &mut params, en));
+                params.planets_enabled = en;
+                let curr_planet = (
+                    params.planets_enabled,
+                    params.planet_count_target,
+                    params.planet_radius_factor,
+                    params.planet_seed,
+                );
+                if curr_planet != prev_planet {
+                    planet_dirty.0 = true;
+                }
+
+                collapsing(ui, "background", "Background", false,
+                    |ui| section_background(ui, &mut params));
+
+                let mut en = params.grid_enabled;
+                collapsing_with_toggle(ui, "grid", "Grid", false,
+                    &mut en,
+                    |ui, en| section_grid(ui, &mut params, en));
+                params.grid_enabled = en;
+            });
+        });
+
+    // egui captures pointer when the cursor is over a window or being
+    // interacted with. MUST stay last — load-bearing for orbit camera.
+    wants.0 = ctx.egui_wants_pointer_input();
 }
diff --git a/src/ui/preset.rs b/src/ui/preset.rs
index ebe77f9..7f954a5 100644
--- a/src/ui/preset.rs
+++ b/src/ui/preset.rs
@@ -10,14 +10,15 @@ use crate::params::{AaQuality, BlackHoleParams, BloomQuality, DiskQuality};
 
 use std::hash::{Hash, Hasher};
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
 pub enum Preset {
-    Cinematic,
-    Performance,
-    Web,
+    #[default]
     /// Read-only marker set when any preset-touched field is hand-edited
     /// away from a preset bundle. `apply(Custom, _)` is a no-op.
     Custom,
+    Cinematic,
+    Performance,
+    Web,
 }
 
 /// The exact params each preset writes. `Custom` writes nothing.